HUDSON – A film of greenish-blue scum on Ottarnic Pond has state environmental officials warning people to avoid contact with the water until bacteria levels return to normal.

The state Department of Environmental Services issued a warning regarding the high levels of cyanobacteria in the pond Aug. 1.

Excess cyanobacteria is evident as greenish-blue clouds or streaks in the water and can produce toxins that can cause health effects that range from skin irritation to chronic liver and central nervous system damage.

The pond doesn’t have a designated beach area, but it has a boat launch and the DES does not recommend any human or animal contact with the water at this time.

Pets also can get sick from the excess bacteria, and should not go in the pond, DES warned.

“Some cyanobacteria produce toxins that ... can cause both acute and chronic health effects that range in severity. Acute health effects include irritation of skin and mucous membranes, nausea, vomiting, and diarrhea. Chronic effects include liver and central nervous system damage,” according to a DES statement.

There are no reports of people or animals becoming ill from contact with the pond.

“More common is that dogs have issues ... nausea, vomiting, diarrhea,”said Sonya Carlson, public beach program coordinator at NH DES.

Carlson said the life cycle of the bacteria is only a few days, and the department will test again this week. DES will post new test results at its beach advisory page, located on its website. The Aug. 1 warning is in effect until new samples can show water quality improvement.

Cyanobacteria naturally exist in the water, but the dangerously high levels could be caused by excess phosphorus in the water, according to DES.

“Generally speaking, there’s runoff from the watershed – all the land that drains to the pond – it washes in everything not nailed down,” Carlson said.

The increase in bacteria levels could be due to animal feces, failing septic or sewage systems, or an overuse of fertilizer.

Residents can have a positive influence on the water quality though, she said.

“Make sure the septic system is working. Properly fertilize, don’t use more than you need,” she said.

Residents closest to the water can plant “buffers,” such as bushes or shrubs to help force runoff through the soil instead of allowing it to wash directly into the pond, Carlson said.

Tina Forbes can be reached at 594-6402 or tforbes@nashuatelegraph.com. Also, follow Forbes on Twitter (@Telegraph_TinaF).